The invention relates to improvements in hydrokinetic torque converters and to improvements in lockup clutches or bypass clutches for use in torque converters. More particularly, the invention relates to improvements in torque converters of the type wherein a rotary housing is provided with a chamber for a pump, a turbine, a stator and lockup clutch having an axially movable annular piston which divides the chamber into a first compartment and a second compartment. The chamber is filled with a suitable fluid (such as oil), and the piston of the lockup clutch carries a first friction surface which can be moved into torque transmitting contact with a second friction surface when the slip clutch is engaged. Still more particularly, the invention relates to improvements in hydrokinetic torque converters and lockup clutches wherein the first compartment is disposed between the piston and a component which carries the second friction surface, and wherein the piston and/or the aforementioned component is provided with one or more passages to establish a path for the flow of fluid from the second compartment substantially radially inwardly toward the rotational axis of the housing.
European Pat. No. 0 078 651 discloses a torque converter having a lockup clutch which includes an annular piston. That side of the piston which faces away from the friction surfaces is provided with channels serving to establish paths for the flow of fluid between a first compartment which is bound by a radial wall of the housing and the piston, and the second compartment which confines the pump and the turbine of the torque converter. The direction of fluid flow is from the second compartment into the first compartment so that the fluid can cool a viscous coupling which transmits torque between the piston and the hub of the turbine.
U.S. Pat. No. 4,969,543 (granted Nov. 13, 1990 to Macdonald for xe2x80x9cSlipping Bypass Clutch Construction for a Hydrokinetic Torque Converterxe2x80x9d) discloses a lockup clutch having an annular piston provided with a first friction surface movable against a second friction surface provided on a radially extending wall of the housing. The piston or the friction lining on the wall of the housing is provided with channels which permit a fluid to flow from the second compartment into the first compartment within the housing even when the lockup clutch is engaged. The channels are provided at the same radial distance from the rotational axis of the housing as the friction surfaces, the first compartment is disposed between the piston and the wall of the housing, and the second compartment accommodates at least the turbine of the torque converter. In the patent the patentee desires to prevent excessive thermal stressing of certain parts of the torque converter such as could develop during continuous slipping of the friction surfaces during operation of the converter. More specifically, the patentee desires to prevent excessive thermal stressing of parts in the region of the two friction surfaces.
Published Japanese patent application No. 58-30532 also discloses a lockup clutch or bypass clutch which is intended for use in a hydrokinetic torque converter and is provided with channels in the region of its friction surfaces.
The aforementioned patent to Macdonald is but one of numerous publications which propose the utilization of a lockup clutch whose friction surfaces slide relative to each other in the disengaged as well as in the engaged condition of the clutch. If the torque converter is installed in the power train of a motor vehicle, the slippage of the friction surfaces forming part of the lockup clutch can be short-lasting (e.g., during shifting into a different gear) or such slippage can be maintained practically within the entire operating range of the torque converter. The extent and the duration of slippage can depend upon the design of the prime mover which drives the housing of the torque converter and/or upon the selected gear ratio and/or upon one or more variable parameters of the prime mover. The lockup clutch dissipates energy in the form of heat during slippage of its friction surfaces relative to each other, and the quantity of dissipated energy can be quite pronounced (e.g., in the range of several kilowatts) during certain stages of operation of the torque converter. Such a situation can develop, for example, when a vehicle pulling a trailer is driven along a mountain road, i.e., the torque converter is apt to dissipate large amounts of energy for an extended period of time. Moreover, when the slip clutch is engaged, the amount of dissipated energy can be greatly increased, at least for a short interval of time, i.e., the torque converter and its lockup clutch are apt to be heated well above a permissible maximum temperature.
The purpose of the establishment of one or more paths for the flow of a fluid coolant is to prevent the aforediscussed drawbacks of heretofore known torque converters and their lockup clutches. A drawback of heretofore known proposals to cool the lockup clutch of a torque converter is that the maximum torque which the lockup clutch can transmit is insufficient, and this is attributable to certain dynamic or kinetic conditions which develop in the fluid flow. The ability of conventional lockup clutches to transmit torque decreases in response to an increasing RPM of the housing of the torque converter as well as in response to increasing rate of fluid flow. This means that, if only the lockup clutch of a heretofore known torque converter is to transmit torque when the RPM of the housing rises to a preselected value, it is necessary to increase the system pressure accordingly. This, in turn, renders it necessary to employ stronger parts, such as a stronger and bulkier piston as well as a higher-capacity pump. Furthermore, the rate of fluid flow per unit of time is then increased again which results in additional losses.
The aforementioned reduction of the ability of the lockup clutches in conventional torque converters to transmit torque is attributable, among other causes, to the development of forces generated as a result of certain dynamic conditions acting upon the radially inwardly flowing fluid in a sense to increase the fluid pressure. Such forces generate a component acting in the direction of the rotational axis of the housing of the torque converter so that the piston is urged to move in a sense to disengage the lockup clutch.
A further drawback of heretofore known undertakings to cool the torque converter in the region of the lockup clutch is that the flow of cooling fluid is overly dependent upon the temperature and/or viscosity of the fluid (such as oil) and/or the difference between fluid pressures at opposite sides of the piston. This means that, if a torque converter and its lockup clutch are constructed and assembled in a manner as proposed, for example, in the aforementioned patent to Macdonald, the resistance to the flow of fluid in the channels between the two fluid-containing compartments must be selected to be satisfactory even under critical circumstances, i.e., the rate of flow of fluid whose temperature has risen to a maximum possible or permissible value is less than the rate at which the system pressure in the torque converter would drop or collapse to an unacceptably low value. In the patented torque converter of Macdonald, the rate of fluid flow in the channels between the two compartments at opposite sides of the piston of the lockup clutch is directly dependent upon the difference between the fluid pressures in the two compartments. Such pressure differential is the variable parameter which controls the transmission of torque by the lockup clutch and, therefore, it cannot be resorted to for the selection of the desired volumetric flow of the fluid. Thus, and in order to maintain the losses in the torque converter above a minimum acceptable value, the rate of fluid flow must be low even when the difference between the fluid pressures in the two compartments rises to a maximum value, i.e., when the converter is called upon to transmit a maximal torque. This may ensure a satisfactory rate of the flow of fluid coolant when the converter is called upon to transmit maximum torque but is unsatisfactory during transmission of lesser torque because the difference between the fluid pressures in the two compartments of the torque converter is too low.
An object of the present invention is to provide a novel and improved torque converter which is capable of transmitting large torques.
Another object of the invention is to provide a hydrokinetic torque converter which can transmit large torques without risking an overheating of its constituents.
A further object of the invention is to provide a conveyance wherein the power train embodies the improved hydrokinetic torque converter.
Still another object of the invention is to provide a torque converter with a lockup clutch or bypass clutch which is constructed and assembled in such a way that it is adequately cooled in the region of its friction surfaces.
A further object of the invention is to provide a torque converter wherein the fluids is not overheated irrespective of the prevailing conditions.
Another object of the invention is to provide a hydrokinetic torque converter wherein the rate of fluid flow in the region of the lockup clutch is not only acceptable but rather highly satisfactory irrespective of the circumstances of use of the torque converter and its lockup clutch.
An additional object of the invention is to enhance the exchange of heat between the parts of the lockup clutch in a hydrokinetic torque converter and a fluid coolant.
Still another object of the invention is to provide a lockup clutch or bypass clutch which is installed in a hydrokinetic torque converter and is constructed and assembled in such a way that the magnitude of torque which the clutch is to transmit can be selected and varied with utmost precision. A further object of the invention is to provide a lockup clutch or bypass clutch which can be utilized in a hydrokinetic torque converter and is constructed and assembled in such a way that the extent of slippage between its friction surfaces can be regulated with a heretofore unknown degree of precision.
Another object of the invention is to provide a lockup clutch which can be installed in the housing of a hydrokinetic torque converter and wherein the slippage between the friction surfaces can be selected with a view to satisfactorily compensating for surges and/or other irregularities of torque transmission regardless of whether the irregularities are attributable to the prime mover which drives the housing of the torque converter and/or to the power train between the prime mover and the housing.
An additional object of the invention is to enhance the comfort of the occupant or occupants of a motor vehicle wherein the power train between the prime mover and the wheels embodies a hydrokinetic torque converter and a lockup clutch or bypass clutch of the above-outlined character.
Still another object of the invention is to provide a novel and improved means for regulating the rate of fluid flow between compartments at opposite sides of the piston in a lockup clutch which is embodied in a hydrokinetic torque transmission.
A further object of the invention is to provide novel and improved piston or pressure plate for use in a lockup clutch of the above-outlined character.
Another object of the invention is to provide novel and improved friction linings for use in the lockup clutches of hydrokinetic torque converters.
An additional object of the invention is to provide a novel and improved housing for use in a hydrokinetic torque converter.
Still another object of the invention is to provide a novel and improved lockup clutch or bypass clutch which can be utilized in a hydrokinetic torque converter and whose operation can be regulated to conform to one or more variable parameters of the torque converter, of the means for driving the torque converter and/or of means receiving torque from the torque converter.
A further object of the invention is to provide a simple, compact and inexpensive torque converter and a simple, compact and inexpensive lockup clutch or bypass clutch for use in such torque converter.
Another object of the invention is to provide a novel and improved method of establishing, dimensioning and orienting fluid flow permitting passages and/or channels in the regions of the friction surfaces in a lockup clutch or bypass clutch for use in hydrokinetic torque converters.
An additional object of the invention is to provide a lockup clutch which can be utilized in the above-outlined novel and improved hydrokinetic torque converter and even in certain types of conventional torque converters.
Still another object of the invention is to provide a lockup clutch wherein the piston or pressure plate can perform one or more important functions in addition to that of engaging and disengaging the clutch.
One feature of the present invention resides in the provision of a hydrokinetic torque converter which comprises a housing which is rotatable about a predetermined axis and is provided with a fluid-containing chamber for the pump, turbine and stator of the torque converter. The latter further comprises a novel and improved engageable and disengageable lockup clutch or bypass clutch which is interposed between the housing and the turbine and comprises an annular piston movable in the chamber In the direction of the predetermined axis and dividing the chamber into a first compartment which is disposed at a first radial distance from the axis and a second compartment. The lockup or bypass clutch (hereinafter called lockup clutch or clutch for short) comprises a first friction surface which is (directly or indirectly) carried by the piston at a second radial distance from the axis greater than the first radial distance and a second friction surface carried by a component which is rotatable with the housing. The first friction surface confronts and is in contact with the second friction surface in the engaged condition of the clutch, and the piston and/or the component has at least one passage for the flow of fluid from the second compartment substantially radially inwardly toward the first compartment. The clutch further comprises first and second members which define at least one channel serving to establish a path for the flow of fluid from the at least one passage into the first compartment and wherein the fluid acts upon the first and/or the second member in the direction of the predetermined axis. Still further, the clutch comprises means for preventing axial movements of the piston in the direction of the predetermined axis in response to the action of the fluid in the at least one channel. Otherwise stated, the first and second members are propped or held relative to each other in the direction of the predetermined axis in such a way that the power flow between them is an endless (closed in itself) flow.
The piston of the lockup clutch is preferably provided with at least one friction lining and the first friction surface is then provided on the at least one friction lining. Furthermore, the first or second member can form part of the piston, i.e., the piston can define the at least one channel jointly with the second or first member. Otherwise stated, one of the first and second members can form part of the piston.
The orientation of the at least one passage can be such that it establishes a path for the flow of fluid from the second compartment toward the first compartment.
The means for preventing axial movements of the piston in the direction of the predetermined axis in response to the action of fluid in the at least one channel can include means for connecting the first and second-members to each other.
In accordance with a presently preferred embodiment, one of the first and second members bounds a portion of the first compartment and is affixed to the aforementioned component or to the piston, and the at least one channel is then provided in the one member.
One of the first and second members can be rigid with (e.g., riveted to or of one piece with) the piston or the component.
The component can include or constitute or form part of a wall which, in turn, forms part of the housing and extends substantially radially of the predetermined axis. The first compartment is disposed between the wall and the piston, as seen in the direction of the predetermined axis.
The piston can be installed between a wall of the housing and the turbine of the torque converter.
If one of the first and second members forms part of the piston, the at least one channel can be provided in the piston.
It is also possible to mount the first or second member on the piston, and the first or the second member can be disposed in the first compartment of the chamber in the housing of the torque converter.
The piston can be disposed in the housing between one of the first and second members and the first compartment.
The pump and the turbine of the torque converter are installed in the second compartment. One of the first and second members can divide the first compartment into two sections which are adjacent each other as seen in the direction of the predetermined axis.
At least one friction lining can be provided on the aforementioned component and/or on the piston. The at least one passage is then adjacent the friction lining, and such passage can be provided in the friction lining.
The inlet of the at least one passage can be disposed at a first radial distance from the predetermined axis, and the outlet of such passage can be disposed at a lesser or shorter second radial distance from the axis.
The width of the first compartment (as measured radially of the predetermined axis) can be selected in such a way that its exceeds the length of the at least one channel. It is presently preferred to select the ratio of the width of the first compartment to the length of the at least one channel in such a way that the length of the channel is not less than 50% of the width of the first compartment.
The at least one passage can constitute a cutout in, or is stamped or embossed into, the friction lining on or of the aforementioned component and/or the piston.
The inlet of the at least one passage can extend substantially parallel with the predetermined axis, and such inlet can be provided in the aforementioned component and/or in the piston. Furthermore, the outlet of the at least one passage can extend substantially parallel with the predetermined axis and can be provided in the piston and/or in the aforementioned component.
The at least one passage in the friction lining on the component and/or on the piston can be configurated in such a way that it establishes a substantially meandering or zig-zag shaped path for the flow of fluid (e.g., oil) between the at least one channel and the second compartment.
If the piston is provided with at least one friction lining having a first portion disposed at a lesser first radial distance and a second portion disposed at a greater second radial distance from the predetermined axis, the at least one passage can be provided in the at least one friction lining in such a way that it has an inlet at least close to one of the first and second portions of the at least one friction lining and an outlet which is at least close to the other of the first and second portions of the at least one friction lining.
The at least one friction lining of the annular piston defines the respective friction surface and can extend substantially circumferentially of the piston. The at least one passage can be provided, at least in part, in the friction lining to extend substantially circumferentially of the piston and to define a substantially meandering or zig-zag shaped path for the flow of fluid between the at least one channel and the second compartment.
If the at least one passage establishes a substantially meandering or zig-zag shaped path for the flow of fluid between the second compartment and the at least one channel, the configuration of the passage is or can be such that it includes at least two turns, i.e., the fluid flowing therein is compelled to change the direction of flow more than once.
As already mentioned above, the piston can comprise or carry at least one friction lining, and the respective friction surface is then provided on such friction lining.
The friction lining of the aforementioned component or of the piston is provided with the respective friction surface, and such friction lining can comprise or can be composed of at least two arcuate sections.
In accordance with another feature of the invention, the lockup clutch can further comprise means for regulating the flow of fluid in the at least one passage as a function of variations of at least one variable parameter of the torque converter. The arrangement can be such that the regulating means controls the flow of fluid in the at least one passage in dependency upon variations of at least one variable parameter of the torque converter and/or as a function of at least one variable parameter of the means (e.g., a combustion engine in a motor vehicle) for driving the housing of the torque converter and/or as a function of at least one variable parameter of the means for receiving torque from the turbine of the torque converter. For example, the torque converter can transmit torque to an automatic transmission in a motor vehicle.
The means for regulating the flow of fluid in the at least one passage can constitute or include an adjustable valve which is installed at the inlet or at the outlet of the at least one passage. Such passage can be defined by a suitably shaped portion of the aforementioned component and/or the piston. The component can constitute a wall, and the at least one passage (or at least one of plural passages) can be defined by a suitably shaped portion of such wall. For example, the at least one passage can be provided in the annular piston, and at least one additional passage can be provided in the piston or in the aforementioned component (such as a wall of the housing).
The valve or any other suitable fluid flow regulating means can be designed in such a way that it includes means for regulating the flow of fluid through the at least one passage to ensure that the rate of fluid flow through the passage is at least substantially constant within the entire operating range of the torque converter.
The pressure of fluid in the first compartment can differ or differs from the fluid pressure in the second compartment during at least one stage of operation of the torque converter, for example, when such torque converter is installed in the power train of a motor vehicle. The aforementioned valve or equivalent means for regulating the flow of fluid in the at least one passage is then designed to regulate the fluid flow as a function of differences between the fluid pressures in the two compartments. The valve is designed to reduce the rate of fluid flow in the at least one passage in response to increasing differences between the fluid pressures in the two compartments.
If the valve is acted upon by centrifugal force in response to rotation of the aforementioned component and/or the piston, it is preferably provided with (or the lockup clutch further comprises) means for varying the rate of fluid flow in the at least one passage as a function of changes of differences between fluid pressures in the first and second compartments and at least substantially independently of the action of centrifugal force.
It has been found that the rate of fluid flow in the at least one passage is quite satisfactory if such rate is different from the square root of the difference between fluid pressures in the first and second compartments.
Another feature of the invention resides in the provision of a hydrokinetic torque converter which comprises (1) a housing having a fluid-containing chamber which is rotatable about a predetermined axis, (2) a pump, (3) a turbine and a stator in the chamber, and (4) an engageable and disengageable lockup clutch which is interposed between the housing and the turbine. The clutch comprises an annular piston movable in the chamber in the direction of the predetermined axis and dividing the chamber into a first compartment and a second compartment. The clutch further comprises a first friction surface which is provided on at least one friction lining of the annular piston, and a second friction surface carried by a component which is rotatable with the housing and serves to confront and contact the first friction surface in the engaged condition of the clutch. The friction surfaces are disposed at a first radial distance from the predetermined axis, and the first compartment is disposed at a lesser second radial distance from such axis. The piston and/or the component is provided with at least one passage for the flow of fluid from the second compartment toward the first compartment in the engaged condition of the clutch, and such passage is disposed at the aforementioned first radial distance from the predetermined axis. The clutch further comprises a wall which is disposed in the first compartment and extends substantially radially of the predetermined axis to define with a second wall at least one channel which establishes a path for the flow of fluid from the at least one passage into the first compartment, and means for connecting the walls to each other against movement relative to one another in the direction of the predetermined axis. The second wall preferably extends at least substantially radially of the predetermined axis.
The second wall can form part of the piston, and the clutch can further comprise means for connecting the first wall to the housing against movement relative to the housing in the direction of the predetermined axis. Still further, the torque converter or its clutch can comprise means for connecting the first wall to the hub of the turbine so that the first wall is held against movement relative to the turbine in the direction of the predetermined axis.
Still another feature of the invention resides in the provision of a novel and improved lockup clutch for use in a hydrokinetic torque converter and comprising a friction lining having at least one friction surface and at least one passage for the flow of a fluid coolant (e.g., oil). The at least one passage is disposed at the at least one friction surface. The ratio of the thickness of the friction lining to the average depth of the at least one passage can be between 1.3 and 2.7. The depth of the at least one passage can be in the range between 0.2 and 0.8 mm, preferably between 0.3 and 0.6 mm.
If the torque converter which embodies the improved lockup clutch is installed in a motor vehicle, the fluid coolant is or can be heated when the vehicle is in actual use, and the at least one passage is or can be configurated in such a way that it ensures the developement of a turbulent coolant flow at its inlet and/or at its outlet when the vehicle is in actual use.
The at least one passage of the improved lockup clutch can extend in the circumferential direction of an annular piston which forms part of the clutch and carries the friction lining. The at least one passage can establish for the fluid coolant a path which is an at least substantially meandering or zig-zag shaped path, and the at least one passage can have an at least substantially constant cross-sectional outline between its inlet and its outlet. The friction lining which defines a substantially meandering or zig-zag shaped path can have a substantially circular shape.
If the improved clutch is embodied in a torque converter having at least one variable operational parameter and being driven by a prime mover (e.g., a combustion engine having one or move variable parameters) to transmit torque to an automatic transmission or another torque receiving unit having one or more variable parameters, the clutch can be further provided with means (e.g., one or more valves or flow restrictors) for regulating the flow of fluid coolant in the at least one passage as a function of variations of at least one of the aforementioned parameters.